1. Field of the Invention
The present invention relates to a rotation angle detection device including a permanent magnet and a magnetic sensing element.
2. Description of Related Art
In recent years, a noncontact rotation angle detection device has been developed that detects the rotation angle of a motor with a permanent magnet and a magnetic sensing element that are disposed apart from each other. Such a rotation angle detection device is described in Japanese Patent Application Publication No. 2014-225998 (JP 2014-225998 A), for example. JP 2014-225998 A describes a motor case, a motor accommodated in the motor case, a first frame (metal plate), a control board (board), and a rotation angle detection device. The motor case is enclosed with the first frame. The control board is disposed above the first frame spaced apart from the first frame. The motor includes a shaft (rotary shaft) passing through the first frame (metal plate) and having an end that protrudes upward from the first frame (metal plate).
The rotation angle detection device includes a magnet (permanent magnet) and a position detection sensor (magnetic sensing element). The magnet is attached to the an end of the shaft. The position detection sensor is mounted on the control board. The magnet and the position detection sensor are disposed so as to face each other.
In such a rotation angle detection device having a structure in which a magnetic sensing element and a permanent magnet face each other as in JP 2014-225998 A, magnetism of the permanent magnet affects circuit components mounted on the board in addition to the magnetic sensing element. Consequently, normal operation of the circuit components may be hindered. Specifically, when a drive circuit of a motor and a control circuit of the drive circuit, etc. are mounted on the board, the drive circuit and the control circuit, etc. may receive the influence of the magnetism of the permanent magnet, thus resulting in malfunction. Meanwhile, magnetism generated by currents flowing in the drive circuit and the control circuit, etc. is detected by the magnetic sensing element. Consequently, distortion, noise, etc. may be generated in detection signals of the magnetic sensing element.